Manufacture of filter plugs



Sept. 3, 1968 D. w. MOLINS I MANUFACTURE; OF FILTER PLUGS Filed April 17. 1967 3,399,606 MANUFACTURE OF FILTER PLUGS Desmond Walter Molins, Deptford, London, England, as-

signor to Molins Machine Company Limited, London, England, a corporation of Great Britain Filed Apr. 17, 1967, Ser. No. 631,421 Claims priority, application Great Britain, Apr. 18, 1966, 16,923/ 66 11 Claims. (Cl. 93-1) ABSTRACT OF THE DISCLOSURE Cigarette filter plug-making equipment in which the degree of stretching imparted to the tow is controlled by an air-permeability detector acting on the unwrapped tow and a beta radiation detector acting on the wrapped filter rod. A rejector mechanism for rejecting defective lengths of filter rod and controlled by the detectors is provided.

Background of the invention This invention relates to the manufacture of filter plugs intended to be combined with cigarettes or similar smoking articles.

Filter plugs are manufactured in the form of a continuous filter rod by wrapping in a continuous paper wrapper a continuous length of filter tow and then cutting off equal lengths from the filter rod. The lengths so cut off are normally multiples of the length of filter plug which will be combined with one cigarette.

The tow consists of a bundle of parallel manmade fibres which, before entering the plug-making machine, passes through plasticising equipment.

The continuous filter rod is made to a nominally constant cross-sectional size and should be of uniform mass per unit length, and the resistance to air flow through the filter rod should also be constant along its length.

The length of filter rod which is combined with a cigarette to form a filter tip cigarette may be in the range of to mm. Therefore, it is important from the smokers point of view that the draw characteristics i.e. the resistance to air flow therethrough, of lengths of filter rod in this range should be reasonably uniform.

The factors influencing the resistance to airflow along a filter rod are (l) the fibre density, by which is meant the number of fibres per unit cross-sectional area (2) the denier of the fibres (3) the degree of crimping of the fibres and (4) the degree of fibre opening or bloom. Some of these factors affect the mass per unit length of the filter rod so that variations of mass per unit length of the filter rod to a certain extent reflect variations in the resistance to airflow along the rod, the higher the mass per unit length of the rod the greater the resistance to airflow through that length of filter rod is likely to present.

If the unwrapped filter tow is of reasonably constant cross sectional area then variations of density of either the unwrapped tow or of the wrapped filter rod will tend to indicate variations in the draw characteristics of the filter rod.

Summary of the invention An object of the present invention is to provide filter plug-making equipment which will produce filter plugs having more uniform draw characteristics.

To this end the invention provides filter plug-making equipment comprising feeding means to stretch a continuous length of filter tow and feed it forwardly, detector means to detect variations in density of the filter tow and produce a signal representing said variations, means for wrapping and sealing a continuous wrapper about the tow to produce a continuous filter rod, means for cutting off lengths of filter rod from the continuous rod, and con- 3,399,5 6 Patented Sept. 3, 1968 trol means responsive to said signal and controlling said feeding means to vary the degree to which the tow is stretched.

The detector means may be downstream of the feeding means and may produce a signal representing short term variations of tow density and the signal may also be utilised to control rejector means to reject lengths of filter rod containing excessive short term variations in density. In this case before being applied to the control means for the feeding means the signal may be smoothed to reduce the short term variations. The detector means may comprise means to produce a flow of air through a length of the unwrapped tow and means to detect variations in pressure drop of the air in passing through the tow caused by variations in air permeability from place to place along the tow.

Alternatively, or in addition, the detector means may comprise means to detect variations in the permeability of the tow to radiation, such as beta radiation.

If both forms of detector are employed the degree of stretch imparted to the tow may be made to be dependent on signals from both detectors. The rejector means may also be controlled by both detectors.

Brief description of the drawing One embodiment of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing of which:

FIGURE 1 shows in diagrammatic side view apparatus according to the invention, and

FIGURE 2 is a detail sectional view on the line 22 of FIGURE 1.

Description of the preferred embodiment The continuous filter tow is shown at FT after it has been processed in plasticising equipment where the fibres of the tow are opened or flutfed out. The tow is stretched and fed into a plug making machine by means of pairs of driven rollers 11, 11 and 12, '12. The pair of rollers 12 are driven at a constant speed, but the pair of rollers 11, 11 are driven at a lower and controlled variable speed so that the tow is stretched between the two pairs of rollers to a variable controlled extent.

The plug making machine is shown diagrammatically at 13. A garniture tape is shown at 14 and the continuous paper wrapper which is drawn into the machine by the garniture tape is shown at 15. Rod-forming mechanism in which the continuous tow is compressed and has the continuous paper wrapper wrapped and sealed about it to form a continuous filter rod FR of nominally constant cross-sectional size is indicated diagrammatically at 16. The cut-off mechanism which severs the continuous filter rod into equal lengths F is indicated at 17. The speed of the tow between the rollers 12, 12 is the same as the speed 01f1 the tow when passing through the plug-making ma- 0 me.

It is found that if the tow FT is wrapped without any correcting action being taken on the tow there are both short-term and long-term variations of both mass per unit length and draw characteristics of the wrapped filter rod.

To detect these variations the following arrangement is adopted. A wheel 18 is provided which has an airpermeable periphery 19 of concave cross section, and a stationary suction chamber 20 is provided within the wheel in communication with a short length of the air-permeable periphery 19. A suction pipe 21 leads from the suction chamber 20 to a suction fan 22 which therefore draws air through the air-permeable periphery 19 into the suction chamber 20. The tow FT is arranged to run in contact with the periphery 19 of the suction wheel 18 over a somewhat greater length of the periphery than the extent of the suction chamber 20 so that all air drawn into the chamher will have first passed through the tow. The wheel 18 is driven at a peripheral speed equal to the linear speed of the tow. Variations in air permeability of the tow will thus produce variations in the rate of flow of air into the chamber 20, and the provision of an air fiow restrictor 21a in the pipe 21, and a pipe 23 connected to the pipe 21 upstream of the restrictor 21a enable variations in air pressure in the chamber caused by these flow variations to be communicated to a transducer 24. The transducer produces an electrical signal which is supplied to a memory unit 25 by means of an electrical connection 26. The air pressure variations in the pipe 23 are also applied to an integrating chamber 27 through a fiow restrictor 28 so that the short term variations in air pressure are smoothed out. The long term air pressure variations in the chamber 27 are applied to a bellows or stack of flexible capsules 29. The bellows or capsules 29 thus expand or contract in conformity with the long term variations of air pressure and are arranged to operate the input member 30 of an hydraulic amplifier 31. The amplifier 31 is as disclosed in US. Patent No. 3,089,497 dated May 14, 1963. The amplifier has an output member 32 which moves under control of the input member 30 but to a magnified extent.

A beta radiation detector is shown at 33. This detects the amount of beta radiation from a source 34 which passes through the wrapped filter rod FR, and produces an electrical signal corresponding to the variations of mass per unit length of the rod FR. In practice, a balancing unit would be provided to give an electrical signal corresponding to the desired mass per unit length of the rod so that the resultant signal produced would be the difference of the two signals and would correspond to the variation of the mass per unit length of the rod FR from the desired mass per unit length. The balancing unit may take the form of another detector and source with a screen interposed to simulate the effect of a filter rod of desired mass per unit length. The beta radiation detector is of high resolution so that its output signal varies with both short and long term variations of mass per unit length of the rod PR. The signal is applied by electrical connections 35 and 35a to the memory unit 25. The signal is also applied by the electrical connection 35 to an integrating device 36 to smooth out the short term variations, and the output signal containing only the long term variations is applied by an electrical connection 37 to a reversible electric motor 38. The motor 38 thus rotates in one direction or the other depending on whether the mean mass per unit length of the rod FR is becoming smaller or greater than the desired mean mass per unit length. The spindle 39 of the motor 38 is threaded and carries a nut 40 which is thus raised or lowered on rotation of the motor 38.

An electric motor 41 drives a shaft 42, which may also be the mainshaft for the plug maker and drive the garniture tape 14. The pair of rollers 12, 12 is driven directly by bevel gears 43, 44, 45 and 46 from the shaft 42, and the pair of rollers 11, 11 is driven by bevel gears 47, 48 from a variable speed reduction gear 49 which in turn is driven by bevel gears 50 and 51 from the shaft 42. The variable speed reduction gear 49 is as disclosed in British patent specification No. 618,774. The gear ratio of the device 49 is altered by member 52.

The output member 32 of the hydraulic amplifier 31, and the nut 40 are pivotally connected to opposite ends of a lever 53, and a link 54 is pivotally connected at one end to an intermediate point on the lever 53 and at its other end to the member 52.

The rollers 11, 11 and 12, 12 are all of the same size and, therefore, as the variable ratio gearing 49 always produces a speed reduction the tow leaving the bite of the rollers 12 is travelling at a greater speed than the speed at which the tow enters the bite of the rollers 11, 11. Thus the tow is stretched between the two pair of rollers, ThiS stretching action reduces the degree of crimping of the tow, and tends to attenuate the fibres, and thus the overall eifect is to reduce the mass per unit length of the tow and thus also to reduce the resistance to air flow therethrough of the wrapped filter rod. Long term increases in mass per unit length of the wrapped filter rod as detected by the detector 33, and long term decreases in air permeability as shown by long term decreases in air pressure in the suction chamber 20 are arrangedto move the member 54 in the same direction. Thus, a long term increase in mass per unit length may be arranged to rotate the motor 38 in the direction so that the nut 40 is raised, and similarly a long term decrease in air pressure in the suction chamber 20 is arranged to move the member 32 upwards. Both of these actions will move the member 54 upwards, and this is arranged to move the member 52 in the direction to increase the gear reduction of the device 49. Thus the speed of the rollers 11, 11 decreases, and the stretching of the tow is increased and has the effect of both reducing the mass per unit length of the wrapped filter rod and increasing its air permeability. Long term decreases in mass per unit of the wrapped filter rod and long term increases in its air permeability produce the opposite effect, the member 52 being lowered to speed up the rollers 11, 11. Thus, long term variations in mass per unit length and in the draw characteristics of the wrapped filter rod are reduced.

There may still be quite large short term variations which cannot be dealt with by varying the amount of stretch imparted to the tow because, as shown, this is essentially a long term control. To cater for variations in either air permeability or mass per unit length which are of such short duration and large amplitude it is arranged that plug lengths P which contain such variations are rejected by rejector mechanism 55. This rejector mechanism, which may be of any known or convenient kind, is controlled by the memory unit 25 which stores information of the location of lengths of tow containing these short term variations and opertates the rejector mechanism 55 when a plug P which contains a defective length of tow is in a position to be operated on by the rejector mechanism 55.

What I claim as my invention and desire to secure by Letters Patent is:

1. Apparatus for producing filter plugs from a continuous length of filter tow comprising feeding means for conveying forwardly a continuous length of filter tow and including means for stretching said continuous length of fil'ter tow while being fed forwardly, detector means to detect variations in density of the filter tow and produce a signal representing said variations, and control means responsive to said signal for controlling said feeding means to vary the degree to which said tow is stretched whereby the density of the filter tow may be maintained constant.

2. Apparatus as claimed in claim 1 wherein the detector means is downstream of the feeding means and comprises means to produce a signal representing shortterm variations of the density, and means to smooth said signal to produce a further signal representing long-term variations of the density, said control means being responsive to said further signal representing long-term variations of the density, said apparatus further comprising means for wrapping and sealing a continuous wrapper about the filter tow to produce a continuous filter rod, means for severing said continuous filter rod into lengths of filter rod, and rejector means responsive to said signal representing the short-term variations of the density to reject lengths of filter rod containing excessive short-term variations in density.

3. Apparatus as claimed in claim 1 wherein the detector means is downstream of the feeding means and comprises means to produce a flow of air through said continuous length of the filter tow and means to detect variations in pressure drop of the air in passing through the tow caused by variations in air permeability from place to place along the tow.

4. Apparatus as claimed in claim 3 wherein the detector means comprises a rotatable wheel having a U- shaped peripheral channel through which the tow runs tangentially thereto and having an air permeable base and suction means for drawing air through the length of tow in the channel.

5. Apparatus as claimed in claim 1 wherein the detector means further comprises means to detect variations in mass per unit length of the filter tow, said latter means comprising a source of beta radiation and means for detecting variations in the permeability of the tow to said beta radiation and produce a signal representing said variations in mass.

6. Apparatus as claimed in claim 5 further comprising means for wrapping and sealing a continuous wrapper about the filter tow to produce a continuous filter rod, means for severing said continuous filter rod into lengths of filter rod and rejector means responsive to said signal representing variations in mass to reject lengths of filter rod containing excessive variations of mass per unit length.

7. Apparatus as claimed in claim 4 wherein said suction means for drawing air through the length of tow in the channel comprises a stationary suction chamber on the side of said air-permeable base opposite said U- shaped peripheral channel.

8. A process for producing a continuous length of filter tow of predetermined substantially constant density comprising feeding a continuous length of filter tow having variable density along its length, determining said variations in density of said filter tow while being fed, and stretching said filter tow to a degree determined by said density variations to reduce the density of any part of said continuous length of filter tow having a density of said predetermined density.

9. A process as claimed in claim 8 wherein said density variations are determined by testing the air permeability of said filter tow.

10. A process as claimed in claim 8 comprisin the further step of determining variations in mass per unit length of said filter tow and stretching said filter tow to a degree deter-mined by said mass variations to reduce the mass per unit length of any part of said continuous length of filter tow having a mass per unit length above a predetermined value, whereby the mass per unit length may be maintained substantially constant.

11. A process as claimed in claim 10 wherein said variations in mass per unit length are determined by testing the permeability of said filter tow to beta radiation.

References Cited UNITED STATES PATENTS 3,035,497 5/1962 Whitehead 93-1 WAYNE A. MORSE, JR., Primary Examiner. 

